The first step of almost every connection on the internet is a DNS query. A client, such as a smartphone, typically uses a DNS server provided by the Wi-Fi or cellular network. The client asks this DNS server to convert a domain name, like www.google.com, into an IP address, like 2607:f8b0:4006:80e::2004. Once the client has the IP address, it can connect to its intended destination.
When the DNS protocol was designed in the 1980s, the internet was a much smaller, simpler place. For the past few years, the Internet Engineering Task Force (IETF) has worked to define a new DNS protocol that provides users with the latest protections for security and privacy. The protocol is called "DNS over TLS" (standardized as RFC 7858).
Like HTTPS, DNS over TLS uses the TLS protocol to establish a secure channel to the server. Once the secure channel is established, DNS queries and responses can't be read or modified by anyone else who might be monitoring the connection. (The secure channel only applies to DNS, so it can't protect users from other kinds of security and privacy violations.)